The present invention relates to an idle stop controlling technique for stopping generation of electricity of a fuel cell system which is mounted on a fuel cell mounted movable body such as automobiles and railroad vehicles.
To improve fuel economy, so-called idle stop control is carried out for a fuel cell vehicle which mounts a fuel cell system. The idle stop control is carried out, for example, by stopping a part of accessories for supplying reaction gas to the fuel cell, such as a compressor, during the stop of the vehicle. For example, Japanese Laid-open Patent Application No. 2001-359204 (see paragraphs [0026] to [0038] and FIGS. 1-5) discloses such idle stop control.
However, even if the fuel cell vehicle stops, idle stop is not preferable in some cases. Japanese Laid-open Patent Application No. 2004-173450 discloses a fuel cell vehicle which determines the cases where idle stop is not preferable and prohibits the stop of supply of reaction gas, namely, prohibits idle stop. In this fuel cell vehicle, electric voltage of each single cell which forms part of the fuel cell is detected, and if the electric voltage lowers, idle stop is prohibited.
In the above fuel cell systems, if the idle stop is carried out during when the operation temperature of the fuel cell is low, acceleration of warming-up operation will be disadvantageously interrupted. This prolongs an unstable cell voltage state, which results in a disadvantage in that response to restart from idling is slow and a smooth running of the fuel cell mounted movable body is impaired. Further, a poor drivability state continues. Idle stop is, however, necessary in terms of improvement in fuel economy.
In view of the above, an object of the present invention is to properly prohibit the idle stop.